GridView:Sorting & Paging Using Generics And Nullable Datatype Function Of C# GetValueOrDefault()

using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Collections.Generic;
/// <summary>
/// Summary description for Sample
/// </summary>
namespace SortingAndPaging
{

    public class Country
    {
        private int m_CountryID = int.MinValue;
        private string m_CountryName = string.Empty;
        private int? m_CountryTradeCode = null;

        public Country()
        {

        }
        public Country(int countryID)
        {
            m_CountryID = countryID;

        }
        public Country(int countryID, string countryName, int? countryTradeCode)
            : this(countryID)
        {
            m_CountryName = countryName;
            m_CountryTradeCode = countryTradeCode;
        }
        public int CountryID
        {
            get { return m_CountryID; }
            set { m_CountryID = value; }
        }
        public int? CountryTradeCode
        {
            get { return m_CountryTradeCode; }
            set { m_CountryTradeCode = value; }
        }
        public string CountryName
        {
            get { return m_CountryName; }
            set { m_CountryName = value; }
        }
        public int CompareTo(Country rhs, Country.CountryComparer.CountryComparisonType which)
        {
            switch (which)
            {
                case CountryComparer.CountryComparisonType.CountryID:
                    return this.m_CountryID.CompareTo(rhs.m_CountryID);
                case CountryComparer.CountryComparisonType.CountryName:
                    return this.m_CountryName.CompareTo(rhs.m_CountryName);
                case CountryComparer.CountryComparisonType.CountryTradeCode:
                    return this.m_CountryTradeCode.GetValueOrDefault().CompareTo(rhs.m_CountryTradeCode.GetValueOrDefault());

            }
            return 0;
        }
        public class CountryComparer : IComparer<Country>
        {
            public enum CountryComparisonType
            {
                CountryID,
                CountryName,
                CountryTradeCode,
                NULL
            }
            private CountryComparisonType _whichComparison;
            private Utility.SortOrder _sortDirection;
            public CountryComparisonType WhichComparison
            {
                get { return _whichComparison; }
                set { _whichComparison = value; }
            }
            public int Compare(Country lhs, Country rhs)
            {
                if (SortDirection == Utility.SortOrder.Asc)
                    return lhs.CompareTo(rhs, WhichComparison);
                else
                    return rhs.CompareTo(lhs, WhichComparison);
            }
            public bool Equals(Country lhs, Country rhs)
            {
                return this.Compare(lhs, rhs) == 0;
            }
            public int GetHashCode(Country e)
            {
                return e.GetHashCode();
            }
            public Utility.SortOrder SortDirection
            {
                get { return _sortDirection; }
                set { _sortDirection = value; }
            }


        }
    }

}